Around this time last year the press was full of impending doom[1]. The winter in Australia (June-Aug 2011) had seen a high level of influenza infection and as it is generally thought that we get what has been circulating there six months earlier the 11/12 influenza season here was predicted to be severe. As it happens the season passed almost unnoticed[2] and, unlike the previous year (1000 calls per hour to NHS direct; shortage of seasonal vaccine etc), there was neither crisis nor comment. How about this year?

The picture in Australia, which is just coming out of the 2012 influenza season, is similar to last year. Influenza spiked early fuelling fears of an epidemic but the number of infections overall has settled to be about the same as the year before[3]. That means that the UK concerns of last year are just as valid this year…. and unfortunately just as unreliable.

The World Health Organisation monitors the strains in circulation to inform the choice for vaccine manufacture, always a mix of three viruses, two influenza A strains and one influenza B. This year the strains are the 2009 H1N1 pandemic virus, previously called swine flu, a 2011 seasonal H3N2 from Australia and a 2010 seasonal flu B (it doesn’t change so much so needs less regular updating)[4]. The relative percentage of these viruses causing actual infections varies from county to country but in the UK last year all three strains were active, albeit at low levels. So the vaccine strains selected match those we have encountered recently and the advice is always to take the seasonal vaccine when it is offered as this in likely to give the best protection for the most probable strains.

An accurate prediction however is all but impossible. One of the factors that frustrate the calculations is the weather. A complex mix of crowding and the longer survival of the virus in the cold and wet conditions mean that the elements play a significant but ill-defined role in virus transmission. Like weather prediction itself, anticipating influenza epidemics is an imperfect science. You can be sure cases of infection will rise in the winter months but when that rise will begin and what level it will reach is much less certain. An unseasonably mild winter like last year may well keep numbers low while an early cold spell, as was the case in 2009/10, will undoubtedly kick off a surge in cases with the concomitant call on surgeries and hospital beds.

At the moment there are no real grounds for suggesting a severe season in the coming winter but there is equally no reason to assume we will get off without some level of infection. The case for vaccination and associated health measures as outlined by the Dept. of Health[5] therefore continues to be appropriate.